This application claims priority to German Patent Application No 10043906.3, filed Sep. 6, 2000, the contents of which are incorporated by reference herein.
This invention relates to a pre-swirl nozzle carrier for an aircraft gas turbine with a body which is provided with a fitted seat for the location of the pre-swirl nozzle carrier on a main carrier and with several rows of pre-swirl nozzles.
In the prior art it is known that in aircraft gas turbines, compressor air is supplied into a disk pre-chamber for the cooling of the blades. The air is supplied via pre-swirl nozzles which enter the disk pre-chamber relatively far outside in the radial direction. The mouth of the pre-swirl nozzle lies near the air supply for blade cooling, enabling a large pressure difference to be used for the supply of cooling air. It is also known in the prior art to arrange the pre-swirl nozzles obliquely to achieve the best possible cooling effect.
It is further known in the prior art to seal the disk pre-chambers radially outwardly and, in particular, radially inwardly to preclude, in particular, the entrance of air or gas into the disk pre-chamber from the inside. This sealing is effected by a conventional labyrinth-type sealing arrangement.
In the designs known in the prior art, an inner seal carrier is arranged radially and thermally freely movable and de-coupled on a main carrier. Centering and support are effected by way of radial spokes. The thermal de-coupling achieved in this way serves the optimization of the seal, in particular the optimization of the thermal behavior.
The known design further provides that the pre-swirl nozzle carrier is located and centered on the main carrier by means of a fitted seat. The axial retention of the inner seal carrier is effected by means of an inner gap of the pre-swirl nozzle carrier.
The known designs result in a relatively irregular, stepped duct which entails an increase in both air volume and friction.
While effective cooling of turbine blading is ensured by the known designs, the air supply via the pre-swirl nozzles prevents the main area of the turbine-disk front wall from being cooled optimally. This suboptimal utilization of the cooling effect results in a relatively high temperature of the turbine disk. This entails, in turn, a decrease of the life of the turbine disk.
A further disadvantage lies in the manufacturing costs. The arrangement according to the prior art incurs a relatively high manufacturing effort, an effect which is generally undesirable.
Furthermore, both the mass and the assembly effort are raised.
In addition, the spokes of the inner labyrinth seal are liable to become inaccurately centered. The reason for this detriment is the clearance afflicted with the spokes. This may result in an increased leakage flow via the labyrinth seal which further increases the temperature in the disk pre-chamber.
In a broad aspect, the present invention provides a pre-swirl nozzle carrier which combines simple design and simple, cost-effective manufacture and assembly with effective cooling of both the turbine blades and the turbine-disk front wall.
It is a particular object of the present invention, to provide a pre-swirl nozzle carrier for a gas turbine, comprising a body with a fitted seat positioned on the body, the fitted seat constructed and arranged to position the pre-swirl nozzle carrier on a main carrier of the gas turbine. A plurality of pre-swirl nozzles are positioned on the body communicating with a disk pre-chamber. The pre-swirl carrier further comprises a body portion extending radially inwardly from the fitted seat to a radially inward side with a plurality of secondary pre-swirl nozzles positioned on the radially inwardly extending body portion and communicating with the disk pre-chamber and a sealing portion positioned on the radially inward side of the body. Further objects and advantageous aspects of the invention will be apparent from the description below.
The pre-swirl nozzle carrier according to the present invention is characterized by a great variety of merits.
The radial inward extension of the body enables an inner seal area and additional secondary pre-swirl nozzles to be provided on its radial inner area. This results in a one-part design which generally is lighter than the two-part design according to the prior art. The one-part design also considerably decreases the assembly effort, in particular since the spokes for the support of the inner sealing area are dispensed with.
The arrangement according to the present invention also provides for optimum centering of the inner sealing area, thereby reducing the leakage flow in this area.
The additional, secondary pre-swirl nozzles according to the present invention provide for effective cooling and temperature decrease at the disk front wall. This increases the life of the disk without impairing the cooling of the turbine blades themselves.
In a particularly advantageous development of the present invention, the body comprises a wall extending axially rearward to a turbine-disk front wall to provide a narrow, smooth-walled disk pre-chamber. This arrangement enables the disk pre-chamber to be designed with a relatively small volume. Accordingly, the disk pre-chamber will contain only a relatively small quantity of air. This is particularly advantageous in terms of the physical processes. While the pre-swirl nozzle carrier is stationary during operation of the turbine, the turbine disk rotates at high speed. This condition generally leads to a temperature increase of the air in the disk pre-chamber. However, the smaller the air volume in the disk pre-chamber, the more favorable the thermal conditions. Accordingly, a decrease of the distance between the pre-swirl nozzle carrier (stator) and the turbine disk (rotor) will reduce the power loss. As becomes apparent, the reduced volume of the disk pre-chamber enables the frictional losses to be decreased, resulting in lesser heating of the air volume.
As opposed to the prior art, the arrangement according to the present invention provides a smooth-walled duct which additionally contributes to the reduction of the air friction. In contrast to this, the duct according to the prior art is irregular, which increases friction.
Therefore, in a particularly favorable design, the wall of the body extends essentially in a radial plane and is essentially smooth at its side facing the turbine-disk front wall. This design provides a narrow, smooth duct through which the pre-swirled air flows from the secondary pre-swirl nozzles. This improves the cooling effect, in particular owing to the reduced frictional losses. Furthermore, the pre-swirled air is kept closely to the disk.
In a further aspect of the present invention, the secondary pre-swirl nozzles are arranged radially inward and axially close to the turbine-disk front wall. This provides for a particularly effective supply of the cooling air enabling both a large area of the disk front wall and areas located further radially inward to be cooled.
The inner seal area preferably comprises a seal carrier and a seal. This provides for a generally optimized design of the pre-swirl nozzle carrier resulting in the advantages in terms of assembly and/or manufacturing costs already described.
In a favorable embodiment of the present invention, the pre-swirl nozzles are arranged obliquely to the axial direction and/or to a radial plane. The same applies for the secondary pre-swirl nozzles.
To further reduce manufacturing costs, it can be particularly beneficial to design the pre-swirl nozzle carrier as a casting. With almost all surfaces producible by casting, mechanical re-machining can essentially be dispensed with. Casting is also appropriate for producing the openings of the pre-swirl nozzles or the secondary pre-swirl nozzles, respectively.
Owing to the optimized thermal conditions, the one-piece design of the pre-swirl nozzle carrier is also beneficial in terms of stress conditons of the entire component. This benefit increases life and reduces the failure risk. By appropriate selection of materials and wall thicknesses, the respective coefficients of expansion can be optimally adapted to the requirements. With the inner seal carrier being one part with the body and, therefore, being centered via the fitting seat as well, improved centering of the inner labyrinth seal and minimized leakage are achieved.
Since the pre-swirl nozzle carrier according to the present invention is located on the main carrier by means of a fitted seat, no additional effort will arise in the case of design changes being made to the main carrier. This is also an essential advantage of the design according to the present invention.
Summarizing, the application of the pre-swirl nozzle carrier according to the present invention provides for a cost reduction by approximately 50 percent over the designs known in the prior art. In addition, it provides for a weight saving of approximately 250 grams.